Printed in Great Britain J. Reprod. Pert., Suppl. 40 (1990), 179-191 ©1990 Journals of Reproduction & Fertility Ltd Uterine and ovarian countercurrentpathways in the control of ovarian function in the pig T. Krzymowski, J. Kotwica and S. Stefanczyk-Krzymowska Department of Reproductive Endocrinology, Centre for Agrotechnology and Veterinary Sciences, 10-718 Olsztyn, Poland Keywords: counter current transfer; ovary; oviduct; uterus; pig Introduction Countercurrent transfer of heat, respiratory gases, minerals and metabolites has been known for many years to be a fundamental regulatory mechanism of some physiological processes. In sea mammals, wading birds and fishes living in polar seas countercurrent systems in the limbs, flippers or tail vessels protect the organism against heat loss (Schmidt-Nielsen, 1981). In most mammals countercurrent heat exchange between the arteries supplying the brain and veins carrying the blood away from the nasal area and head skin forms the so-called brain cooling system, which protects the brain against overheating (Baker, 1979). The countercurrent transfer of minerals and metab- olites in the kidney is a well-known system regulating the osmolarity and concentration of urine (Lassen & Longley, 1961). Countercurrent transfers in the blood vessels of the intestinal villi take part in the absorption processes (Lundgren, 1967). The pampiniform plexus in the boar partici- pates in a heat-exchange countercurrent, thus decreasing the temperature of the testes (Waites & Moule, 1961), as well as in local transfer of testosterone (Free et al., 1973; Ginther et al., 1974; Einer-Jensen & Waites, 1977). Studies on the influence of hysterectomy on the function of the corpus luteum in different species, made in the 1930-1970s, suggested the existence of a local transfer of a luteolytic substance from the uterus to the ovary. These suggestions have been con- firmed by detailed and elegant anatomical papers of the vascular anatomy of the uterus, ovary and oviduct in mares (Ginther et at, 1972), cows (Ginther & Del Campo, 1974), ewes (Ginther et at, 1973; Del Campo & Ginther, 1973), sows (Del Campo & Ginther, 1973) and laboratory animals (Del Campo & Ginther, 1972). Ginther (1974) suggested that there was a local transfer of a luteo- lytic substance from the uterus to the ovary. The experiments of McCracken et al. (1972) on sheep were critical for understanding the mechanism of transfer of prostaglandins. Using radioactive prostaglandin they proved for the first time the existence of the local transfer of prostaglandin from the utero-ovarian vein to the ovarian artery. Moreover, the countercurrent transfer of radioactive inert gases was demonstrated in laboratory animals (Einer-Jensen, 1974), of progesterone in sheep (McCracken & Einer-Jensen, 1976; Einer-Jensen & McCracken, 1981; Walsh et at, 1979) and pigs (Krzymowski et at, 1981b; Kotwica et at, 1981), of testosterone in pigs (Krzymowski ci at, 198Ia; Krzymowski et al., 1981b) and cows (Kotwica et at, 1982), of oestradiol in pigs (Krzymowski et at, 1981b) and cows (Krzymowski et at, 1981/1982; Koziorowski et at, 1988), of relaxin and thyroxin in ewes (Schramm et at, I986a), and of oxytocin in sheep (Schramm et at, I986b) and cows (Koziorowski et at, 1989). The morphological adaptation of the walls of adjacent arterial and venous vessels (Lee & O'Shea, 1975; Doboszynska et at, 1980) and the relationship between countercurrent efficiency and the size of hormone molecules (McCracken et al., 1984) have been investigated in the context of the countercurrent mechanism. Kotwica (1980) suggested that the lymph and lymphatic vessels in sows participated in prostaglandin transfer in the area of the mesovarium. Heap et al. (1985) 180 T. Krzymowski et al demonstrated that PGF-2a transfer from the uterine lymph into the ovarian vasculature in sheep was potentially as great as that from the uterine venous blood. Einer-Jensen (1984, 1988) suggested a relationship between the countercurrent transfer of hor- mones and hormones binding to plasma proteins. As far as is known, the pool of free steroids in the blood plasma is maintained in equilibrium with the pool of carrier-bound hormones, with only I- 2% of steroid hormones being in the unbound form in the arterial blood. According to Liner- Jensen (1984, 1988) the local transfer of free hormone from the veins and lymphatic vessels to the artery, even at a low efficiency of countercurrent exchange, can considerably multiply the concen- tration of free hormone in arterial blood that is able to interact with the receptor. Moreover, it was suggested that the less polar (ketonic) member of each steroid pair was transferred more efficiently than its hydroxyl counterpart. This may be due to its greater solubility in the membrane lipids of the cells in the interposing vessel walls (McCracken et at, 1984). Role of the broad ligament of the uterus in the countercurrent transfer of hormones Mesovarium In sows the ovarian artery is subdivided into several basic branches in the mesovarium area. After division, one of them reaches the mesosalpinx and oviduct and provides the mesovarian muscular layer with numerous tiny ramifications. Two or three middle branches form many loops on the surface of and near the ovarian vein, and some of them anastomose with the uterine artery. The ramifications of convoluted branches go deep into the vessel plexus and surrounding muscular layer. All the vessels are covered with a muscular layer which is especially well developed in the ovarian area. Lymph drains from the ovary through numerous tiny lymphatic vessels situated immediately under the perimetrium covering the muscles. This network of lymphatic vessels is drained in turn by large valved vessels deep in the convoluted arterial branches (T. Krzymowski, unpublished observations). The rhythmic contractions of the muscular layer of the mesovarium results in changes of the venous blood and lymph flow (T. Krzymowski, unpublished observations). The muscular layer of the broad ligament is supplied with the arterial blood that passes through the fine, short arterial ramifications that leave the branches of the ovarian artery at right angles. These arterial ramifi- cations penetrate the muscular layer of the mesovarium and create a capillary bed. The blood from the muscular layer returns through fine, short veins which, reaching the branches of the ovarian artery, redivide on the arterial surface or pass by to connect with the venous network covering the arteries (Fig. I). The origin of the network covering the branches of the ovarian arteries is still not clear. Lee & O'Shea (1975) suggested that in ewes this venous network was supplied with uterine blood. In sows a fine venous network covering the walls of the ovarian artery branches has been described in detail (Figs 2a, b). It was functionally associated with countercurrent transfer of steroid hormones and prostaglandins in the area of the mesovarium (Krzymowski et at, I982a; Kotwica et at, 1982/ 1983). The venous network was found to twine around the artery covering more than half of the surface of the ovarian artery branches (Fig. 2b). It is only loosely associated with the surface of the adjacent arterial walls and can be easily removed. Spontaneous or mechanically stimulated contractions of a section of the convoluted branches of the ovarian artery were studied during in-situ experiments which restricted blood flow through the venous network covering the contracting section (T. Krzymowski, unpublished observations). The nervous and hormonal regulation of blood flow through the convoluted branches of the ovarian artery, as well as through the venous network covering the branches, may therefore be an important component of the countercurrent mechanism of the mesovarium area. In 1976, McCracken & Einer-Jensen showed for the first time the possibility of progesterone countercurrent transfer in the mesovariurn in ewes. In sows, tritiated testosterone introduced into C'ountercurroIl Itonsjecr in the broad ligament 181 Ovoy Lymph from ovary. high cony of Lief( 1/hormones 0 -0 Ridnah Ovarian Murree ar ayer or Me ovrinan vam of m00000111110 aocry Fig. 1. Diagram of the blood circulation in the mesovarium showing the morphological con- ditions for two steps in the transfer of steroid hormones_ First step: from the lymph (high steroid concentration) into the capillaries of the muscular layer supplied with the systemic blood (low steroids concentration). Second step: from the venous network (high concentration) cos cring the branches of the ovarian artery into the arterial blood (low concentration). (Adapted from Krzymowski et al., 19821). the ovarian vein was found in high concentrations in the ovarian artery (Krzymowski et al., 1979). Many experiments on the ovary isolated with the mesovarium and supplied by the autologous blood proved tha t testosterone, oestradiol and progesterone were transferred from the ovarian vein to the artery in the mesovarium area (Krzymowski eu al., 1981a, h, I982a, Id: Kotwica ci a/ 1981). The dynanncs of steroid uptake and retention in the mesovarium after infusion o f [1 Hltestosterone into the ovarian vein was studied by Stebinczyk (1984). The capacity for total binding of 0-ljtestosterone in the mesovarium was considerably higher than in other parts of the broad ligament. High values of [TI]testosterone in the eytosol were mostly hound by albumin and a,- globulin. but the absence of [11-Iltestosterone in the nuclear fraction suggested that binding was not receptor mediated (Stefanczyk, 1984). The transfer of testosterone, oestrahol and progesterone from the venous effluent lo the ovarian artery in sows turned attention to the role of lymph in this arca. The concentration of steroids in the ovarian lymphatic outflow in sows has not been investigated under physiological conditions in rim During experiments on the ovary isolated with the osarian pedicle, the steroid concentrations were higher in the lymph and interstitial fluid than in the venous blood (Kotwica ci al., 1981). In ewes, chronic cannulation of the utero-ovarian lymph ducts ipsilateral to the (-Amy bearing the corpus luteum showed tha t the concentration of progesterone in lymph was 182 T.